Function histogram_hunks 

pub fn histogram_hunks(
    old: &str,
    new: &str,
    file_path: &str,
    context: u32,
    indent_heuristic: bool,
) -> Vec<Hunk>

Histogram hunks of old vs new, merged the way git merges nearby hunks. We seed ids like crate::git so staging finds the hunk it shows.